Human Transfiguration can be used to essentially replicate the natural abilities of Metamorphmagi, allowing the practitioner or the subject to take on an entirely different form or make various individual changes to their appearance, such as growing or changing the colour of one's hair[2] or taking on individual animal body parts. However, while human Transfiguration can presumably be performed by any wizard who's skilled enough, on themselves as well as on others, a Metamorphmagus is born with the ability to make such changes to their own bodies with little to no effort and without the use of a wand[3].

Although it is possible to transfigure humans into inanimate objects[4], it is unknown how someone who had himself transfigured into an object would be able to untransfigure without the intervention of another witch or wizard.

Dangers

It has been stated many times that human Transfiguration can go badly wrong when performered poorly. The user has the risk of getting stuck in his or her's transfigured state.

"Harry turned and saw something monstrous cutting through the water toward them: a human body in swimming trunks with the head of a shark.... It was Krum. He appeared to have transfigured himself — but badly."

While competing in the second task of the Triwizard Tournament, Viktor Krum attempted to transfigure himself fully or partially into a shark; ultimately, only his head was transfigured, the shark's teeth were misplaced[4].

According to Nymphadora Tonks, her Metamorphmagus abilities gave her an advantage in the Disguise and Concealment portion of Auror training, as Aurors have to transfigure and untransfigure themselves on a regular basis[2].